The present invention relates to an isolated DC amplifier circuit and, in particular, to a DC amplifier circuit with transformer coupled isolation, which is employed for transmitting DC signals from the input side to the output side of a circuit whose potentials with respect to ground differ from each other.
For the above purpose, a magnetic operational amplifier circuit, a modulation type DC amplifier circuit with modulation feedback, and a pulse width transmission type DC amplifier circuit have been employed. However, these circuits are complex, large in size and power consumption, and slow in operating speed. Further, these circuits are significantly influenced by noise because of a large stray capacitance caused by numerous insulating portions and the large size of the circuit. Still further, these circuits cannot be used in severe conditions, because of a great many circuit elements, some of which have their operating characteristics changed by ambient conditions.